I've improved the PoC a lot for this, an updated video-replay.c is attached. This version does not require the binary patch for the sender binary, other than adding the library with insert_dylib. So to use this one:
1) Build video-replay.c attached (g++ -std=c++11 -g -dynamiclib -o mylib video-replay.c) and copy to /usr/lib/mylib
2) Use insert_dylib (https://github.com/Tyilo/insert_dylib) to add /usr/lib/mylib to AVConference (insert_dylib --strip-codesig /usr/lib/mylib AVConference)
3) Edit /System/Library/Sandbox/Profiles/com.apple.avconferenced.sb to add /out as allow file read and write
4) Restart the machine
5) Extract the attached out.zip to /out and change the permissions so it's readable by AVConference
6) Call target with FaceTime, when they pick up, AVConference will crash